Guard against nested allows with ref name caching

This avoids the case:

```
allow_ref_name_caching do
  allow_ref_name_caching do
    # using-feature
  end
end
```

app/models/ci/pipeline.rb

@@ -781,7 +781,7 @@ module Ci
     end
 
     def git_ref
-      strong_memoize(:git_pref) do
+      strong_memoize(:git_ref) do
         if merge_request_event?
           ##
           # In the future, we're going to change this ref to

lib/gitlab/gitaly_client.rb

@@ -302,6 +302,7 @@ module Gitlab
     # branch, this method allows caching of the ref name directly.
     def self.allow_ref_name_caching
       return yield unless Gitlab::SafeRequestStore.active?
+      return yield if ref_name_caching_allowed?
 
       begin
         Gitlab::SafeRequestStore[:allow_ref_name_caching] = true